RNA-protein interactions are important in many cellular functions, including transcription. RNA splicing, and translation. One example of such an interaction is the mechanism of trans-activation of the human immunodeficiency virus type 1 (HIV-1) gene expression that requires the interaction of Tat protein with the trans-activation responsive region (TAR) RNA, a 59-base stem-loop structure located at the 5xe2x80x2-end of all nascent HIV-1 transcripts1.
The promoter of HIV-1, located in the U3 region of the viral long terminal repeat (LTR), is an inducible promoter which can be stimulated by the trans-activator protein, Tat1. As in other lentiviruses, Tat protein is essential for trans-activation of viral gene expression2-6.
Tat-derived peptides containing the arginine-rich RNA-binding domain of Tat are able to form in vitro complexes with TAR RNA7-14. Structural studies of Tat protein show that the RNA-binding domain is not a rigid helix15. Since the RNA-binding domain of Tat has a flexible structure, the symmetry of small peptides containing arginine-rich sequences may not be crucial in TAR RNA recognition. Recent syntheses of two D-enantiomeric proteins demonstrated that these proteins have optical properties, substrate specificity16, and a structure17,13 that mirrors those of the naturally occurring L-proteins. A powerful method to identify D-peptide ligands through mirror-image phage display has been recently discovered and a cyclic D-peptide was identified that interacts with the Src homology 3 domain of c-Src19. Due to the difference in chirality, D-peptides are resistant to proteolytic degradation and cannot be efficiently processed for major histocompatibility complex class II-restricted presentation to T helper cells (TH cells). Consequently, D-peptides would not induce a vigorous humoral immune response that impairs the activity of L-peptide drugs20.
The present invention concerns Tat-inhibitory polypeptide derivatives. More particularly, this invention relates to polypeptides of the formula I
D-Cys-D-Phe-D-Thr-D-Thr-D-Lys-D-Ala-D-Leu-D-Gly-D-Ile-D-Ser-D-Tyr-D-Gly-D-Arg-D-Lys-D-Lys-D-Arg-D-Arg-D-Gln-D-Arg-D-Arg-D-Arg-D-Pro-D-Pro-D-Gln-D-Gly-D-Ser-D-Gln-D-Thr-D-His-D-Gln-D-Val-D-Ser-D-Leu-D-Ser-D-Lys-D-Gln (SEQ ID 1)
and fragments and analogs thereof, and the biologically and pharmaceutically acceptable salts thereof, which exhibit advantageous properties, including binding to xcex94TAR, inhibition of LTR-dependent reporter gene expression in a model cell assay and, finally, inhibition of HIV-1 replication, as determined in assays of HIV-induced syncytium formation, cytotoxicity and reverse transcriptase production. These compounds are thus useful in the treatment of HIV-1 infection by virtue of their ability to block the interaction of Tat protein with TAR RNA, thereby interfering with the transactivation step in the replication cycle of HIV-1. The rationale for this approach is that such peptides compete with the full length Tat protein for binding to TAR RNA, thereby preventing the required interactions between other domains in Tat protein and the nascent transcription apparatus.
It is an object of the present invention to provide compounds which are useful in the treatment of HIV-1 by virtue of their ability to block the interaction of Tat protein with TAR RNA, thereby interfering with the trans activation step in the replication cycle of this virus.
It is further an object of this invention to provide pharmaceutical compositions suitable for the administration of such compounds.
It is a still further object of the present invention to provide a method of treating HIV-1 infection in mammals which comprises the administration of the compounds of the present invention.